Defect-fluorite oxides M1-yLnyO2-y/2(Ln = lanthanide; M = Hf, Zr, Ce, U, Th): Structure, property, and applications

An up-to-date summary of our coupled macroscopic (lattice parameter, a 0 ) and microscopic (Mössbauer) studies on the entitled systems is given, shedding new light on the basic phase and structure properties of these technologically important, highly defective oxides. Through these studies, the intermediate-pyrochlore (P)-based local structure nature of the so-called stabilized-zirconia (SZ)- and stabilized-hafnia (SH)-type defect-fluorite (DF) phases in the M 4+ = Zr and Hf systems seems to be almost unambiguously established with different (from the conventional) approaches: These are (1) the presence of a broad lattice parameter ( a 0 ) hump over the extended stabilized cubic DF region ( y = ~0.3-~0.7); (2) the microscopic 151 Eu-Mössbauer evidence of Eu 3+ isomer shifts (ISs) showing characteristic V-shaped minima around the ideal-P area ( y ~ 0.50) for both the M 4+ = Zr and Hf systems; and (3) rich 155 Gd-Mössbauer data on the Zr 1- y Gd y O 2- y /2 system [IS, quadrupole splitting (QS), line width, peak height, and relative absorption area (RAA)], revealing detailed features of its ordered P-disordered DF phase and structure relationships. These results are discussed with reported basic-property data of these systems.